Should charge variants of monoclonal antibody therapeutics be considered critical quality attributes?

Coupling cation and anion exchange chromatography for fast separation of monoclonal antibody charge variants

A design procedure for the separation of charge variants of a monoclonal antibody (mAb) was developed, which was based on the coupling of cation-exchange chromatography (CEX) and anion-exchange chromatography (AEX) under high loading conditions. The design of the coupled process was supported by a dynamic model. The model was calibrated on the basis of band profiles of variants determined experimentally for the mAb materials of different variant compositions. The numerical simulations were used to select the coupling configuration and the loading conditions that allowed for efficient separation of the mAb materials into three products enriched with each individual variant: the acidic (av), main (mv) and basic (bv) one. In the CEX section, a two-step pH gradient was used to split the loaded mass of mAb into a weakly bound fraction enriched with av and mv, and a strongly bound fraction containing the bv-rich product. The weakly bound fraction was further processed in the AEX section, where the mv-rich product was eluted in flowthrough, while the av-rich product was collected by a step change in pH. The choice of flow distribution and the number of columns in the CEX and AEX sections depended on the variant composition of the mAb material. For the selected configurations, the optimized mAb loading density in the CEX columns ranged from 10 to 26 mg mL-1, while in the AEX columns it was as high as 300 or 600 mg mL-1, depending on the variant composition of the mAb material. By proper selection of the loading condition, a trade-off between yield and purity of the products could be reached.

Isolation and characterization of rabies monoclonal antibody charge variants

Current postexposure prophylaxis of rabies includes vaccines, human rabies immunoglobulin (RIG), equine RIG, and recombinant monoclonal antibodies (mAb). In the manufacturing of rabies recombinant mAb, charge variants are the most common source of heterogeneity. Charge variants of rabies mAb were isolated by salt gradient cation exchange chromatography (CEX) to separate acidic and basic and main charge variants. Separated variants were further extensively characterized using orthogonal analytical techniques, which include secondary and tertiary structure determination by far and near ultraviolet circular dichroism spectroscopy. Charge and size heterogeneity were evaluated using CEX, isoelectric focusing (IEF), capillary-IEF, size exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blotting. Antigen binding affinity was assessed by enzyme linked immuno-sorbent assay and rapid florescence foci inhibition test. Results from structural and physicochemical characterizations concluded that charge variants are formed due to posttranslational modification demonstrating that the charge heterogeneity, these charge variants did neither show any considerable physicochemical change nor affect its biological function. This study shows that charge variants are effective components of mAb and there is no need of deliberate removal, until biological functions of rabies mAb will get affected.

LC-MS Characterization and Stability Assessment Elucidate Correlation Between Charge Variant Composition and Degradation of Monoclonal Antibody Therapeutics

Aggregation stability of monoclonal antibody (mAb) therapeutics is influenced by many critical quality attributes (CQA) such as charge and hydrophobic variants in addition to environmental factors. In this study, correlation between charge heterogeneity and stability of mAbs for bevacizumab and trastuzumab has been investigated under a variety of stresses including thermal stress at 40 °C, thermal stress at 55 °C, shaking (mechanical), and low pH. Size- and charge-based heterogeneities were monitored using analytical size exclusion chromatography (SEC) and cation exchange chromatography (CEX), respectively, while dynamic light scattering was used to assess changes in hydrodynamic size. CEX analysis revealed an increase in cumulative acidic content for all variants of both mAbs post-stress treatment attributed to increased deamidation. Higher charge heterogeneity was observed in variants eluting close to the main peak than the ones eluting further away (25-fold and 42-fold increase in acidic content for main and B1 of bevacizumab and 19-fold for main of trastuzumab, respectively, under thermal stress; 50-fold increase in acidic for main and B1 of bevacizumab and 10% rise in basic content of main of trastuzumab under pH stress). Conversely, variants eluting far away from main exhibit greater aggregation as compared to close-eluting ones. Aggregation kinetics of variants followed different order for the different stresses for both mAbs (2nd order for thermal and pH stresses and 0th order for shaking stress). Half-life of terminal charge variants of both mAbs was 2- to 8-fold less than main indicating increased degradation propensity.

Statistically-aided development of protein A affinity chromatography for enhancing recovery and controlling quality of a monoclonal antibody

Protein A chromatography is widely used for isolation of monoclonal antibodies (mAbs) from cell culture components. In this study, the effect of different process parameters of the Protein A purification namely, binding pH, elution pH, flow rate, neutralization pH and tween concentration, on the concentration and quality of the purified mAb were evaluated. Using design of experiments approach, the critical process parameters of protein A chromatography were identified and experimentally optimized. Their impact on quality attributes, such as size variants and charge variants, of the mAb was studied. Multivariate data analysis was subsequently performed using multiple linear regression and partial least squares regression methods. It was observed that the elution pH primarily governed the concentration of the purified mAb and the content of monomers and aggregates, while the tween concentration primarily influenced the main peak of the charge variants. This is the first study that evaluates the impact of tween concentration in buffers on the protein A chromatography purification step. These studies helped in identifying the design space and defining the target robust and optimal setpoints of the responses, which were subsequently verified experimentally. These setpoints not only passed the target criteria but also resulted in the highest recoveries during the investigation. Through this statistically-aided approach, an optimized and robust protein A chromatography process was rationally developed for purification of mAbs, while achieving the desired product quality. This study highlights the influence of multiple parameters of the protein A purification process on critical quality attributes of mAbs, such as the size and charge variants, which has been a very scarcely explored area.

Imaged capillary isoelectric focusing associated with multivariate analysis: A powerful tool for quality control of therapeutic monoclonal antibodies

Monoclonal antibodies are increasingly used in cancer therapy. To guarantee the quality of these mAbs from compounding to patient administration, characterization methods are required (e.g. identity). In a clinical setting, these methods must be fast and straightforward. For this reason, we investigated the potential of image capillary isoelectric focusing (icIEF) combined with Principal Component Analysis (PCA) and Partial least squares-discriminant analysis (PLS-DA). icIEF profiles obtained from monoclonals antibodies (mAbs) analysis have been pre-processed and the data submitted to principal component analysis (PCA). This pre-processing method has been designed to avoid the impact of concentration and formulation. Analysis of four commercialized mAbs (Infliximab, Nivolumab, Pertuzumab, and Adalimumab) by icIEF-PCA led to the formation of four clusters corresponding to each mAb. Partial least squares-discriminant analysis (PLS-DA) applied to these data allowed us to build models to predict which monoclonal antibody is analyzed. The validation of this model was obtained from k-fold cross-validation and prediction tests. The selectivity and the specificity of the model performance parameters were assessed by the excellent classification obtained. In conclusion, we established that the combination of icIEF and chemometric approaches is a reliable approach for unambiguously identifying compounded therapeutic monoclonal antibodies (mAbs) before patient administration.

High-throughput capillary electrophoresis analysis of biopharmaceuticals utilizing sequential injections

The complexity of biotherapeutic products implies an ever-increasing list of product quality attributes that need to be monitored and characterized. In addition, the growing interest in implementing process analytical technology in biopharmaceutical production has further increased the testing burden, together with the need for rapid testing that can facilitate real-time or near-real-time decision-making. Capillary electrophoresis (CE) has made a place in biopharmaceutical analysis but is regarded as a low-throughput method, with the instrument dead time constituting more than 80% of the total time of analysis. In this study, the dead time of CE was utilized to analyse 3 mAb samples in a single-CE run. This approach resulted in an up to 77% reduction in the total analysis time and increased the productivity by up to 300%, compared to traditional single CE-ultraviolet runs, without compromising resolution or relative peak areas. Additionally, good method reproducibility was observed. The compatibility of the method has been demonstrated with protein A eluate and cation exchange chromatography fractions. We, thus, propose that sequential injections can be applied for fast and robust CE analysis of biopharmaceuticals.

Enhanced cell growth, production, and mAb quality produced in Chinese hamster ovary-K1 cells by supplementing polyamine in the media

Polyamines such as putrescine (PUT), spermidine (SPD), and spermine (SPM) are amine group-containing biomolecules that regulate multiple intracellular functions such as proliferation, differentiation, and stress response in mammalian cells. Although these biomolecules can be generated intracellularly, lack of polyamine-synthesizing activity has occasionally been reported in a few mammalian cell lines such as Chinese hamster ovary (CHO)-K1; thus, polyamine supplementation in serum-free media is required to support cell growth and production. In the present study, the effects of biogenic polyamines PUT, SPD, and SPM in media on cell growth, production, metabolism, and antibody quality were explored in cultures of antibody-producing CHO-K1 cells. Polyamine withdrawal from media significantly suppressed cell growth and production. On the other hand, enhanced culture performance was achieved in polyamine-containing media conditions in a dose-dependent manner regardless of polyamine type. In addition, in polyamine-deprived medium, distinguishing metabolic features, such as enriched glycolysis and suppressed amino acid consumption, were observed and accompanied by higher heterogeneity of antibody quality compared with the optimal concentration of polyamines. Furthermore, an excessive concentration of polyamines negatively affected culture performance as well as antibody quality. Hence, the results suggest that polyamine-related metabolism needs to be further investigated and polyamines in cell growth media should be optimized as a controllable parameter in CHO cell culture bioprocessing. KEY POINTS: • Polyamine supplementation enhanced cell growth and production in a dose-dependent manner • Polyamine type and concentration in the media affected mAb quality • Optimizing polyamines in the media is suggested in CHO cell bioprocessing.

Trastuzumab Charge Variants: a Study on Physicochemical and Pharmacokinetic Properties

Background

Post-translational modifications in bioprocessing and storage of recombinant mAbs are the main sources of charge variants. While the profile of these kinds of variants is considered an important attribute for the therapeutic mAbs, there is controversy about their direct role in safety and efficacy. In this study, the physicochemical and pharmacokinetic (PK) properties of the separated charge variants belonging to a trastuzumab potential biosimilar, were examined.

Methods

The acidic peaks, basic peaks, and main variants of trastuzumab were separated and enriched by semi-preparative weak cation exchange. A panel of analytical techniques was utilized to characterize the physicochemical properties of these variants. The binding affinity to HER2 and FcγRs and the PK parameters were evaluated for each variant.

Results

Based on the results, the charge variants of the proposed biosimilar had no significant influence on the examined efficacy and PK parameters.

Conclusion

During the development and production of biosimilar monoclonal antibodies, evaluating the effect of their charge variants on efficacy and PK parameters is needed.

Digital twin of a continuous chromatography process for mAb purification: Design and model-based control

Model-based design of integrated continuous train coupled with online process analytical technology (PAT) tool can be a potent facilitator for monitoring and control of Critical Quality Attributes (CQAs) in real time. Charge variants are product related variants and are often regarded as CQAs as they may impact potency and efficacy of drug. Robust pooling decision is required for achieving uniform charge variant composition for mAbs as baseline separation between closely related variants is rarely achieved in process scale chromatography. In this study, we propose a digital twin of a continuous chromatography process, integrated with an online HPLC-PAT tool for delivering real time pooling decisions to achieve uniform charge variant composition. The integrated downstream process comprised continuous multicolumn capture protein A chromatography, viral inactivation in coiled flow inverter reactor (CFIR), and multicolumn CEX polishing step. An online HPLC was connected to the harvest tank before protein A chromatography. Both empirical and mechanistic modeling have been considered. The model states were updated in real time using online HPLC charge variant data for prediction of the initial and final cut point for CEX eluate, according to which the process chromatography was directed to switch from collection to waste to achieve the desired charge variant composition in the CEX pool. Two case studies were carried out to demonstrate this control strategy. In the first case study, the continuous train was run for initially 14 h for harvest of fixed charge variant composition as feed. In the second case study, charge variant composition was dynamically changed by introducing forced perturbation to mimic the deviations that may be encountered during perfusion cell culture. The control strategy was successfully implemented for more than ±5% variability in the acidic variants of the feed with its composition in the range of acidic (13%-17%), main (18%-23%), and basic (59%-68%) variants. Both the case studies yielded CEX pool of uniform distribution of acidic, main and basic profiles in the range of 15 ± 0.8, 31 ± 0.3, and 53 ± 0.5%, respectively, in the case of empirical modeling and 15 ± 0.5, 31 ± 0.3, and 53 ± 0.3%, respectively, in the case of mechanistic modeling. In both cases, process yield for main species was >85% and the use of online HPLC early in the purification train helped in making quicker decision for pooling of CEX eluate. The results thus successfully demonstrate the technical feasibility of creating digital twins of bioprocess operations and their utility for process control.

Design and optimization of membrane chromatography for monoclonal antibody charge variant separation

The manufacturing scale implementation of membrane chromatography to purify monoclonal antibodies has gradually increased with the shift in industry focus towards flexible manufacturing and disposable technologies. Membrane chromatography are used to remove process-related impurities such as host cell proteins and DNA, leachates and endotoxins, with improved productivity and process flexibility. However, application of membrane chromatography to separate product-related variants such as charge variants has not gained major traction due to low binding capacity. The work reported here demonstrates that a holistic process development strategy to optimize static binding (pH and salt concentration) and dynamic process (membrane loading, flowrate, and gradient length) parameters can alleviate the capacity limitations. The study employed high throughput screening tools and scale-down membranes for intermediate and polishing purification of the model monoclonal antibody. An optimized process consisting of anion exchange and cation exchange membrane chromatography reduced the acidic variants present in Protein A eluate from 89.5 % to 19.2 % with 71 % recovery of the target protein. The membrane chromatography process also cleared host cell protein to below limit of detection with 6 to 30-fold higher membrane loading, compared to earlier reported values. The results confirm that membrane chromatography is effective in separating closely related product variants when supported by a well-defined process development strategy.

A Charge Variant of Bevacizumab Offers Enhanced FcRn-Dependent Pharmacokinetic Half-Life and Efficacy

BACKGROUND

Lysine variants of monoclonal antibodies (mAbs) result from incomplete clipping of the C-terminal lysine residues of the heavy chain. Although the structure of the lysine variants has been determined for several mAb products, a detailed study that investigates the impact of lysine charge variants on PK/PD and preclinical safety is yet to be published.

OBJECTIVE

An in-depth investigation of the impact of C- terminal lysine clipping of mAbs on safety and efficacy for bevacizumab charge variants.

METHOD

Charge variant isolation using semi-preparative chromatography is followed by a comparative analysis of FcRn binding, pharmacokinetics, and pharmacodynamics in relevant animal models.

RESULTS

K1 variant exhibited improved FcRn binding affinity (4-fold), half-life (1.3-fold), and anti-tumor activity (1.3-fold) as compared to the K0 (main) product. However, the K2 variant, even though exhibited higher FcRn affinity (2-fold), displayed lower half-life (1.6-fold) and anti-tumor activity at medium and low doses. Differential proteomic analysis revealed that seven pathways (such as glycolysis, gluconeogenesis, carbon metabolism, synthesis of amino acids) were significantly enriched. Higher efficacy of the K1 variant is likely due to higher bioavailability of the drug, leading to complete downregulation of the pathways that facilitate catering of the energy requirements of the proliferating tumor cells. On the contrary, the K2 variant exhibits a shorter half-life, resulting only in partial reduction in the metabolic/energy requirements of the growing tumor cells.

CONCLUSION

Overall, we conclude that the mAb half-life, dosage, and efficacy of a biotherapeutic product are significantly impacted by the charge variant profile of a biotherapeutic product.

Analytical Similarity Assessment of Biosimilars: Global Regulatory Landscape, Recent Studies and Major Advancements in Orthogonal Platforms

Biopharmaceuticals are one of the fastest-growing sectors in the biotechnology industry. Within the umbrella of biopharmaceuticals, the biosimilar segment is expanding with currently over 200 approved biosimilars, globally. The key step towards achieving a successful biosimilar approval is to establish analytical and clinical biosimilarity with the innovator. The objective of an analytical biosimilarity study is to demonstrate a highly similar profile with respect to variations in critical quality attributes (CQAs) of the biosimilar product, and these variations must lie within the range set by the innovator. This comprises a detailed comparative structural and functional characterization using appropriate, validated analytical methods to fingerprint the molecule and helps reduce the economic burden towards regulatory requirement of extensive preclinical/clinical similarity data, thus making biotechnological drugs more affordable. In the last decade, biosimilar manufacturing and associated regulations have become more established, leading to numerous approvals. Biosimilarity assessment exercises conducted towards approval are also published more frequently in the public domain. Consequently, some technical advancements in analytical sciences have also percolated to applications in analytical biosimilarity assessment. Keeping this in mind, this review aims at providing a holistic view of progresses in biosimilar analysis and approval. In this review, we have summarized the major developments in the global regulatory landscape with respect to biosimilar approvals and also catalogued biosimilarity assessment studies for recombinant DNA products available in the public domain. We have also covered recent advancements in analytical methods, orthogonal techniques, and platforms for biosimilar characterization, since 2015. The review specifically aims to serve as a comprehensive catalog for published biosimilarity assessment studies with details on analytical platform used and critical quality attributes (CQAs) covered for multiple biotherapeutic products. Through this compilation, the emergent evolution of techniques with respect to each CQA has also been charted and discussed. Lastly, the information resource of published biosimilarity assessment studies, created during literature search is anticipated to serve as a helpful reference for biopharmaceutical scientists and biosimilar developers.

Exploring the limits of conventional small-scale CHO fed-batch for accelerated on demand monoclonal antibody production

In the field of therapeutic antibody production, diversification of fed-batch strategies is flourishing in response to the market demand. All manufacturing approaches tend to follow the generally accepted dogma of increasing titer since it directly increases manufacturing output. While titer is influenced by the biomass (expressed as IVCD), the culture time and the cell-specific productivity (q_P), we changed independently each of these parameters to tune our process strategy towards adapted solutions to individual manufacturing needs. To do so, we worked separately on the increase of the IVCD as high seeding fed-batch capacity. Yet, as intensified fed-batch may not always be possible due to limited facility operational mode, we also separately increased the q_P with the addition of specific media additives. Both strategies improved titer by 100% in 14 days relative to the standard fed-batch process with moderate and acceptable changes in product quality attributes. Since intensified fed-batch could rival the cell-specific productivity of a conventional fed-batch, we developed novel hybrid strategies to either allow for acceptable seeding densities without compromising productivity, or alternatively, to push the productivity the furthest in order to reduce timelines.

Applications of capillary electrophoresis for biopharmaceutical product characterization

Capillary electrophoresis (CE), after being introduced several decades ago, has carved out a niche for itself in the field of analytical characterization of biopharmaceutical products. It does not only offer fast separation, high resolution in miniaturized format, but equally importantly represents an orthogonal separation mechanism to high-performance liquid chromatography. Therefore, it is not surprising that CE-based methods can be found in all major pharmacopoeias and are recommended for the analysis of biopharmaceutical products during process development, characterization, quality control, and release testing. Different separation formats of CE, such as capillary gel electrophoresis, capillary isoelectric focusing, and capillary zone electrophoresis are widely used for size and charge heterogeneity characterization as well as purity and stability testing of therapeutic proteins. Hyphenation of CE with MS is emerging as a promising bioanalytical tool to assess the primary structure of therapeutic proteins along with any impurities. In this review, we confer the latest developments in capillary electrophoresis, used for the characterization of critical quality attributes of biopharmaceutical products covering the past 6 years (2015-2021). Monoclonal antibodies, due to their significant share in the market, have been given prioritized coverage.

Ion Exchange Chromatographic Methods for Purification of Therapeutic Antibodies

Ion Exchange Chromatography has been a critical unit operation for manufacturing of therapeutic antibodies. Cation and anion exchange chromatography are used extensively to remove process-related as well as product-related impurities to obtain the final product. In this chapter, we describe the methods for separating and purifying charge variants and aggregates for manufacturing of monoclonal antibodies. The methods related to removal of host cell impurities such as host cell DNA and host cell proteins are also described. With minimal modifications, the protocols described here can be employed to purify any monoclonal antibody.

A simple, rapid, and robust "on-the-go" identity testing of biotherapeutics using FTIR spectroscopy

The stunning rise of biotherapeutics as successful treatments of complex and hard-to-treat diseases, in particular cancer, has necessitated the development of a rapid analytical method capable of differentiating these otherwise significantly similar antibody-based products. The existing methods for product identification pose significant drawbacks in terms of the consumption of time and labor. Here, we present an FTIR spectroscopy-based simple, rapid, and robust method that is capable of differentiating between the biotherapeutics (both innovator products and biosimilars). The proposed approach uses partial least-squares-discriminant analysis to pinpoint subtle differences in the FTIR spectra of the samples, enabling us to not only identify the product but also calculate its concentration. This FTIR-based method can be used to fulfill the identity testing requirement of a pharmaceutical drug in its final packaged form set by the US Food and Drug Administration. Along with this, identity testing can also be deployed at multiple steps in the manufacturing process and can also be used by the appropriate regulatory or government agency for tackling counterfeits of biotherapeutic products.

Effect of vitamins and metal ions on productivity and charge heterogeneity of IgG1 expressed in CHO cells

Recombinant monoclonal antibodies have emerged as the most successful modality of biotherapeutics. They are primarily expressed in Chinese Hamster Ovary (CHO) cells. It is well known that post-translational modifications (PTM) contribute significantly to heterogeneity with respect to charge, glycosylation, and size. These attributes in turn impact stability, pharmacokinetics, and pharmacodynamics of the biotherapeutic product. Cell culture media components are known to significantly contribute to both cellular productivity as well as post-translational modifications. Thus, it is highly desirable to understand how media components affect product quality. This study aims to explore the impact of vitamins and metal ions on protein expression and post-translational modifications specifically charge heterogeneity. Biotin, choline chloride, D-calcium pantothenate, folic acid, pyridoxine hydrochloride, thiamine hydrochloride vitamins and Fe, Cu, Mg, Co, Zn, Mn, Ni metal ions were examined in this study. The results indicate that pyridoxine enhances productivity while Zn, Cu, Fe, Mn, and biotin impact charge heterogeneity. While, Fe, Mn and Ni enhance production of the acidic variants, Cu and biotin inhibit it. Zn reduces formation of basic variants while biotin enhances it. The results from this investigation could be used for process control so as to get consistent charge variant profile, in particular for biosimilars.

Freeze thaw and lyophilization induced alteration in mAb therapeutics: Trastuzumab as a case study

Long-term stability of therapeutic monoclonal antibody (mAb) products is necessary for their successful commercialization. Freeze-thaw (F/T) operations are often performed for a mAb product during processing, storage and distribution. Lyophilization (Lyo) is another unit operation that is commonly used for drug product manufacturing of mAbs. This paper aims to explore the impact of these operations on structure and function of a mAb therapeutic, as well as of biosimilars. Trastuzumab innovator and its five biosimilars were analysed for aggregation, charge heterogeneity, secondary structure, binding kinetics, and potency after each freeze-thaw and lyophilization cycle. It is observed that both F/T and Lyo induce protein aggregation, which in turn causes perturbations in the biological potency of the mAb therapeutic. The average value of the percentage of aggregation increased from 0.6 % (week 1) to 5.3 % (week 10) in F/T study and from 0.8 % (week 1) to 10.1 % (week 10) in Lyo study. The acidic pool increased from 26.5 % (week 1) to 44.4 % (week 10) and the basic variants from 13.9 % (week 1) to 24.0 % (week 10) in F/T study. Similarly, acidic pool increased from 27.1 % (week 1) to 42.0 % (week 10) and basic variants from 14.8 % (week 1) to 24.4 % (week 10) in Lyo study. The average percentage of beta-sheet increased from 58.4 % (week 1) to 60.9 % (week 10) in F/T study and from 59.7 % (week 1) to 72.6 % (week 10) in Lyo study. Lower binding affinity was found in week 7 as compared to week 1 in Lyo study whereas no change in binding affinity was observed in the F/T study. The average potency value gradually decreased from 0.97IU/ ml (week 1) to 0.75IU/ ml (week 10) in F/T study and from 1.0IU/ ml (week 1) to 0.66IU/ ml (week 10) in Lyo study. Results indicate that lyophilization has a bigger impact on binding affinity than freeze thaw and as expected, the impact was comparable across the innovator and biosimilar products.

LC-MS based case-by-case analysis of the impact of acidic and basic charge variants of bevacizumab on stability and biological activity

The present study investigates the impact of charge variants on bevacizumab's structure, stability, and biological activity. Five basic and one acidic charge variants were separated using semi-preparative cation exchange chromatography using linear pH gradient elution with purity > 85%. Based on the commercial biosimilar product's composition, two basic variants, one acidic and the main bevacizumab product, were chosen for further investigation. Intact mass analysis and tryptic peptide mapping established the basic variants' identity as those originating from an incomplete clipping of either one or both C-terminal lysine residues in the heavy chain of bevacizumab. Based on peptide mapping data, the acidic variant formation was attributed to deamidation of asparagine residue (N84), oxidation of M258, and preservation of C-terminal lysine residue, located on the heavy chain of bevacizumab. None of the observed charge heterogeneities in bevacizumab were due to differences in glycosylation among the variants. The basic (lysine) variants exhibited similar structural, functional, and stability profiles as the bevacizumab main product. But it was also noted that both the variants did not improve bevacizumab's therapeutic utility when pooled in different proportions with the main product. The acidic variant was found to have an equivalent secondary structure with subtle differences in the tertiary structure. The conformational difference also translated into a ~ 62% decrease in biological activity. Based on these data, it can be concluded that different charge variants behave differently with respect to their structure and bioactivity. Hence, biopharmaceutical manufacturers need to incorporate this understanding into their process and product development guidelines to maintain consistency in product quality.

Fractionated charge variants of biosimilars: A review of separation methods, structural and functional analysis

The similarity between originator and biosimilar monoclonal antibody candidates are rigorously assessed based on primary, secondary, tertiary, quaternary structures, and biological functions. Minor differences in such parameters may alter target-binding, potency, efficacy, or half-life of the molecule. The charge heterogeneity analysis is a prerequisite for all biotherapeutics. Monoclonal antibodies are prone to enzymatic or non-enzymatic structural modifications during or after the production processes, leading to the formation of fragments or aggregates, various glycoforms, oxidized, deamidated, and other degraded residues, reduced Fab region binding activity or altered FcR binding activity. Therefore, the charge variant profiles of the monoclonal antibodies must be regularly and thoroughly evaluated. Comparative structural and functional analysis of physically separated or fractioned charged variants of monoclonal antibodies has gained significant attention in the last few years. The fraction-based charge variant analysis has proved very useful for the biosimilar candidates comprising of unexpected charge isoforms. In this report, the key methods for the physical separation of monoclonal antibody charge variants, structural and functional analyses by liquid chromatography-mass spectrometry, and surface plasmon resonance techniques were reviewed.

Comparative analytical profiling of bevacizumab biosimilars marketed in India: a national control laboratory study

In this study, analytical profiling of the bevacizumab (BVZ) biosimilars (N = 3) approved in India were evaluated for charge heterogeneity, isoelectric focusing, aggregation and in vitro potency analysis. The charge variants were characterized using high performance cation-exchange chromatography (CEX-HPLC), capillary zone electrophoresis (CZE) and capillary isoelectric focusing (cIEF). cIEF was also used for estimation of isoelectric point (pI value). In addition, aggregate analysis was done using size exclusion high performance chromatography (SEC-HPLC). The cell-based inhibition of proliferation assay using HUVEC cells, indirect ELISA and Western blot were performed for in vitro biological activity. In addition of cell-based cytotoxicity assay was also performed and found no cytotoxic effect on both HuT78 and WIL2S cells by bevacizumab biosimilars. The significant variations in acidic (p < 0.0001) and basic variants (p < 0.0001), pI value (p = 0.0035), aggregates (p = 0.0306) of biosimilars were found as compared to innovator product; however, cell-based potency analysis (p = 0.6047) and indirect ELISA (p = 0.1611) have shown no significant difference in the biological activity. The banding patterns of all biosimilars in western blot were found similar to the innovator product. The comparatively higher basic variants in the biosimilars were attributing to the high pI value of biosimilars to that of innovator product, although these variations were not affecting the biological activity of the biosimiars. This is a unique study, wherein the independent analysis by a National Control Laboratory (NCL) will not only help the National Regulatory Authority (NRA) to assess the quality and consistency in manufacturing of BVZ biosimilars marketed in India but also facilitate the uptake of BVZ biosimilars, and sustainable access to new medicines against the anti-angiogenic therapy.

Impact of linker-drug on ion exchange chromatography separation of antibody-drug conjugates

Charge variants are important attributes of monoclonal antibodies, including antibody-drug conjugates (ADCs), because charge variants can potentially influence the stability and biological activity of these molecules. Ion exchange chromatography (IEX) is widely used for charge variants analysis of mAbs and offers the feasibility of fractionation for in-depth characterization. However, the conjugated linker-drug on ADCs could potentially affect the separation performance of IEX, considering IEX separation relies on surface charge distribution of analyte and involves the interaction between analyte surface and IEX stationary phase. Here, we investigated weak cation exchange chromatography (WCX) for its application in analyzing three ADCs (two broad distribution ADCs and an ADC with controlled conjugation sites) and the 2-drug/4-drug loaded species isolated from the two broad distribution ADCs using hydrophobic interaction chromatography. The major peaks in WCX profile were characterized via fraction collection followed by capillary electrophoresis-sodium dodecyl sulfate or peptide mapping. Results suggested that both the number of drug loads and conjugation sites could impact WCX separation of an ADC. The hypothesis was that the linker drugs could interfere with the ionic interaction between its surrounding amino acids on the mAb surface and column resin, which reduced the retention of ADCs on WCX column in this study. Our results further revealed that WCX brings good selectivity towards positional isomers, but limited resolution for different drug load, which causes the peak compositions of the two broad-distribution ADCs to be highly complex. We also compared results from WCX and imaged capillary isoelectric focusing (icIEF). Results showed that separation in icIEF was less influenced by conjugated linker drugs for the ADCs studied in this work, and better alignment was found between the two techniques for the ADC with controlled conjugate sites. Overall, this work provides insights into the complexity of WCX analysis of ADCs, which should be considered during method development and sample characterization.

Impact of mammalian cell culture conditions on monoclonal antibody charge heterogeneity: an accessory monitoring tool for process development

Recombinant monoclonal antibodies are predominantly produced in mammalian cell culture bioprocesses. Post-translational modifications affect the micro-heterogeneity of the product and thereby influence important quality attributes, such as stability, solubility, pharmacodynamics and pharmacokinetics. The analysis of the surface charge distribution of monoclonal antibodies provides aggregated information about these modifications. In this work, we established a direct injection pH gradient cation exchange chromatography method, which determines charge heterogeneity from cell culture supernatant without any purification steps. This tool was further applied to monitor processes that were performed under certain process conditions. Concretely, we were able to provide insights into charge variant formation during a fed-batch process of a Chinese hamster ovary cell culture, in turn producing a monoclonal antibody under varying temperatures and glucose feed strategies. Glucose concentration impacted the total emergence of acidic variants, whereas the variation of basic species was mainly dependent on process temperature. The formation rates of acidic species were described with a second-order reaction, where a temperature increase favored the conversion. This platform method will aid as a sophisticated optimization tool for mammalian cell culture processes. It provides a quality fingerprint for the produced mAb, which can be tested, compared to the desired target and confirmed early in the process chain.

Assessment of structural and functional similarity of biosimilar products: Rituximab as a case study

Biosimilars are products that are similar in terms of quality, safety, and efficacy to an already licensed reference/ innovator product and are expected to offer improved affordability. The most significant source of reduction in the cost of development of a biosimilar is the reduced clinical examination that it is expected to undergo as compared to the innovator product. However, this clinical relief is predicated on the assumption that there is analytical similarity between the biosimilar and the innovator product. As a result, establishing analytical similarity is arguably the most important step towards successful development of a biosimilar. Here, we present results from an analytical similarity exercise that was performed with five biosimilars of rituximab (Ristova®, Roche), a chimeric mouse/ human monoclonal antibody biotherapeutic, that are available on the Indian market. The results show that, while the biosimilars exhibited similarity with respect to protein structure and function, there were significant differences with respect to size heterogeneity, charge heterogeneity and glycosylation pattern.